Hackers recently broke into payment systems at several northwestern U.S. restaurants and food service companies via a remote access account belonging to one of their vendors, another example of the need for companies to monitor third-party access to their networks.

Information Systems and Supplies (ISS), a Vancouver, Wash.-based provider of point of sale (PoS) systems to restaurants and bars in the region, has warned its customers that hackers may have accessed their payment systems using ISS' remote login credentials.

ISS President Thomas Potter said a LogMeIn account used by the company to remotely support and manage customer network was thrice breached between Feb. 28 and April 18. LogMeIn technology lets systems administrators and service providers like ISS remotely login to customer servers and PCs.

"We have reason to believe that the data accessed could include credit card information from any cards used by your customers between these dates," Potter said in a letter addressed to ISS clients last month.

Prior to the intrusion, ISS used a common password to access its LogMeIn account, allowing the hackers to easily log in to payment networks of multiple ISS customers, he said. After the breach, the company instituted separate passwords for accessing individual customer accounts, Potter noted.

ISS has also worked with customers to identify and remove the malware from their networks, he said.

A security vendor and the U.S. Secret Service are investigating the scope and nature of the breach.

The incident illustrates the need for businesses to keep a constant eye on third-party access to their networks. In recent years, numerous companies have opened up their networks to vendors, partners, suppliers and others to streamline business processes and enable better service and support.

Few, though, implement standards or processes for governing third-party access to their networks.

The massive data compromise at Target for instance, began when a hacker gained access to one of the retailer's systems via a remote access account belonging to a heating, ventilation and air conditioning company. Hackers were able to use that access to gain a foothold on an internal system and then use that to leapfrog to other systems inside Target's network.

Trustwave last year estimated that 63% of 450 data breaches studied by the security vendor were caused by security vulnerabilities that were introduced by a third party.

Small businesses and franchises within the food and beverage industry and the retail sector were most often impacted by third-party security failures, according to Trustwave. "Many third-party vendors leave the door open for attack, as they don't necessarily keep client security interests top of mind," Trustwave concluded.